In the composites reinforcement industry, and in particular, the fiber side of the industry, where common fibers are glass, carbon, aramid (Kevlar) and the like, there is a need to transition these fibers from their “as-built” state to process dispensing in the most efficient manner. The term “efficient” in this disclosure means both dispensing with the minimum disturbance and in an “untwist fashion”.
In the fiberglass industry in the US, dominated by Owens Corning, PPG, Vetrotex, and FGI, there is a process in which a “doff” of fiberglass is automatically made in a 24 hour-per-day operation. Molten glass in an elevated furnace is allowed to drop naturally through Platinum bushings and is cooled and consolidated into thousands of glass filaments that make up a single “tow”. This tow may have sizing added, but the tow can be traveling at 100 miles per hour as it exits the Platinum bushings.
This tow is in a flattened “wet” state (from sizing solutions) that allow it to be formed into a band as it is automatically wound up onto a temporary mandrel of paper or cardboard sleeve material in a very precise wound pattern. This wound pattern quickly increases from approximately 4-6 inches in inside diameter to approximately 10-11 inches in outside diameter in perhaps 2-3 minutes. A glass doff, when completed may weigh approximately 40 lbs. and have 3 miles of glass tow wound around the temporary cardboard or paper sleeve or inside mandrel.
When a doff is completed in the automatic winding process, a laborer will manually remove the finished 40-lb doff and stack it on a pallet. Once a pallet of wet doffs is completed they will be sent to a large drying operational room, and left to dry the wet sizing for many hours. After a set time the “dry” doffs are removed from the room and they are taken to a final prep-to-ship area. Here a laborer will remove the temporary sleeve from the inside of the doff and may actually discharge manually a layer (or two) of fiberglass that is not fully dry. Shrink wrap will be put on the outside of the doff for handling and shipping and the doff will be stacked onto a pallet for shipping. Doffs produced in this way are known as center-pull doffs, since they require dispensing of tows from the inside to the outside of the doff.
This doff is then sold to a processor such as a pultrusion manufacturer, weaving or stitching manufacturer, or any of about 30 different types of “composite processors” where it is combined with resins and a composite will be formed (this obviously an over-simplified explanation of “processing”). All of these processors remove the fiberglass doff from the shipping pallet and stack the doff onto a shelf, rack, or horizontal surface, and then the manufacturer dispenses a single tow from one doff, along with hundreds, or even thousands of tows from like doffs, and processes all tows in parallel into a composite of some shape and design.
This action is referred to as “Center-Pull”, since the doff by its very nature requires and demands dispensing from the inside outward. The tow is pulled from the inside of the doff and naturally unwinds in a twisted fashion as it pulls out from the inside diameter (ID) of the doff. Much as a coiled hose, being pulled longitudinally from a coiled state, these generally flat bands of fiberglass tows perform the same physical twisting. With every rotation around the inside diameter of the doff, there is exactly one twist that is imparted to the fiberglass band. This natural twist can have detrimental performance attributes when formed in a composite. The location of the twist can provide a localized void as the filaments cannot stretch. Thus the tow bands have edge filaments that must naturally buckle the interior filaments at the location of a twist. This reduces fiber volume and minimized the quantity of filaments that can be consolidated in a given cross sectional area.
Processors of fiber doffs, including fiberglass doffs, have recognized for some time the need for providing untwisted fiber. They therefore have demanded that the fiber manufacturers rewind a manufactured “virgin” center-pull doff. The doff described above is “virgin” because it exists undisturbed following the initial winding from the furnace bushing and the subsequent drying. Filaments as small as 8-13 microns made from these materials can be very prone to fracture when handled or disturbed. In spite of this problem, processors have asked glass manufacturers to rewind these virgin doffs so that the tows can be dispensed in a less twisted or untwisted state.
This rewind process is interesting. This is because the glass manufacturer takes a virgin doff and installs said doff onto an expensive and sophisticated machine, wherein the inside of the doff is mounted onto the machine and then the doff (with Shrink-wrap removed) is spooled and rotated and the tow is rewound onto a spool from outside-to-inside, creating what is known in the industry as a tangent spool. This tangent spool can be used by a processor such as a filament winder to dispense from the outside of the tangent spool in an untwisted tow fashion, to get the desired results in performance from a composite, with zero twist in the tow.
These tangent spools are typically about ½ the weight of a center-pull doff. But the manufacturer will charge anywhere from 5-10 cents per lb. or more to do this rewinding. The processor also knows that after the doff has been rewound into this tangent spool, that this action is one more step in handling the fiber and that it is likely there will be broken filaments and, thus, degraded strength in the sum of all the filaments that make up the tow.
Machines adapted for handling tangent spools include filament winders and tangent pull dispensing tooling. In order to allow a doff to be placed onto such devices, the fiber manufacturer has to rewind the doff onto a tangent-pull cardboard sleeve of the correct diameter accepted by such machines. As stated, it is well-known in the industry that this rewinding of glass fibers creates some loss in performance, as this secondary handling will undoubtedly break fiber-filaments and affect the structural strength of the end product. Additionally, the rewinding requires labor and time, and it is not unusual for a fiber manufacturer to add 5-10 cents per lb. or more, to the price of a rewound spool of glass fiber, over the price of a “virgin” center-pull doff.
In Applicants prior U.S. Pat. No. 7,690,179 (U.S. application Ser. No. 11/771,919 which claims priority from Prov. App. No. 60/945,853), the contents of which are incorporated herein by reference, an untwist device was disclosed using a novel rotating table, activated by a control system, to dispense tows in an untwisted fashion from an original, center-pull doff. This device has been commercialized. However, there are some restrictions and difficulties in locating turntables in manufacturing-process plants.